CN110643948A - Strontium titanate/ruthenate strontium ferroelectric superlattice thin film material and preparation method thereof - Google Patents
Strontium titanate/ruthenate strontium ferroelectric superlattice thin film material and preparation method thereof Download PDFInfo
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Abstract
The invention aims to provide a strontium titanate/strontium ruthenate ferroelectric superlattice thin film material and a preparation method thereof. The strontium titanate/ruthenate strontium ferroelectric superlattice thin film material of the invention is a high-performance lead-free ferroelectric material, and the residual polarization strength of the thin film material reaches 33.0 mu C/cm2Is 750% higher than that of traditional lead-free ferroelectric material barium titanate film, and may be used together with lead zirconate titanate (Pb (Zr)xTi1‑x)O3) The lead-based ferroelectric thin film material is comparable to the lead-based ferroelectric thin film material. The preparation method of the material comprises the steps of alternately growing strontium ruthenate and strontium titanate on a single crystal substrate by using a pulse laser deposition method, and accurately regulating and controlling the period thickness of the superlattice by controlling the time of laser bombardment on different target materials. Strontium titanate/ruthenate strontium ferroelectric superlattice film material as high-performance lead-free ferroelectric materialSubstituted Pb (Zr)xTi1‑x)O3The lead-based ferroelectric film has wide application prospect in ferroelectric memories, sensors, actuators and other integrated ferroelectric devices.
Description
Technical Field
The invention belongs to the field of electronic information materials, functional materials and intelligent materials, and particularly relates to a strontium titanate/strontium ruthenate ferroelectric superlattice thin film material and a preparation method thereof.
Background
The ferroelectric film is an important electronic information material, functional material and intelligent material, and can be made into ferroelectric material due to its excellent ferroelectric, piezoelectric, pyroelectric and dielectric propertiesRandom access memory, sensor, actuator, transistor field effect transistor, surface acoustic wave device, pyroelectric detector, etc. At present, lead zirconate titanate (Pb (Zr) is a common ferroelectric materialxTi1-x)O3PZT for short) as a representative lead-based oxide ceramic material. Since lead-based ferroelectric materials contain a large amount of PbO, there is a risk of serious pollution to the ecological environment during production, use and disposal thereof. In recent years, in order to cope with the problem of global increasing environmental pollution, the main countries in the world have successively issued pollution control management methods about the prohibition of use of certain harmful substances in electronic and electric equipment and electronic information products. Among them, lead-containing ferroelectric and piezoelectric materials are limited in use. Therefore, the development and application of "environmentally friendly" lead-free ferroelectric materials are not only an important scientific and technical problem, but also have become social problems with much attention.
In recent years, there have been some advances in the development and application of lead-free ferroelectric materials. However, compared with the traditional PZT lead-based ferroelectric material, the lead-free ferroelectric material has larger differences in ferroelectric, piezoelectric, dielectric and other properties. Therefore, the development of a lead-free ferroelectric material with high performance, which can reach or even exceed the performance of the traditional PZT lead-based ferroelectric material, is a key problem that must be solved for realizing the replacement of the lead-based ferroelectric material by the lead-free ferroelectric material.
Strontium titanate (SrTiO)3) The quantum paraelectric insulator has a cubic perovskite structure (c ═ a), and does not have ferroelectricity. However, some external factors can damage SrTiO3The symmetry of the lattice inversion in space makes it ferroelectric, so SrTiO3Also known as initial ferroelectrics. It is reported that SrTiO can be made by A-site ion doping, isotopic substitution, strain effect, and the like3Ferroelectricity occurs. In addition, SrTiO grown under low oxygen pressure3The epitaxial film has large tetragonality (c/a)>1) And lattice volume, room temperature ferroelectricity can also occur. However, in SrTiO by these methods3The ferroelectricity induced by the method is very small compared with the traditional ferroelectric material, so that the method does not have the advantages of low cost and high efficiencyHas practical value. However, we have found that SrTiO3And strontium ruthenate (SrRuO)3) The superlattice thin film material formed by the composition material has excellent iron polarization performance. In SrTiO3/SrRuO3In the superlattice thin film material, SrRuO3Thickness is controlled to be 2 unit cells, SrTiO3The thickness is controlled to be 25 unit cells, and the residual polarization intensity is as high as 33.0 mu C/cm2Compared with the traditional lead-free ferroelectric material BaTiO3The film contrast is increased by nearly 750 percent, and can be compared favorably with a lead-based ferroelectric material PZT film. The method has important significance for the development and application of the lead-free ferroelectric film material.
Disclosure of Invention
The invention aims to provide a strontium titanate/ruthenate strontium ferroelectric superlattice thin film material and a preparation method thereof. The material consists of a strontium titanate layer and a strontium ruthenate layer which are periodically grown, and has good ferroelectric property: the residual polarization intensity reaches 33.0 mu C/cm2. The strontium titanate/ruthenate strontium ferroelectric superlattice thin film material is prepared by adopting a pulse laser deposition method, and is characterized in that the process is simple, and the period thickness of the superlattice thin film can be accurately regulated and controlled, so that the ferroelectric property of the superlattice thin film can be continuously regulated and controlled. The ferroelectric superlattice thin film material is used as a high-performance lead-free ferroelectric material, and has wide application prospect in integrated ferroelectric devices such as memories, sensors, actuators and the like.
The invention specifically provides a strontium titanate/ruthenate strontium ferroelectric superlattice thin film material, which is characterized in that: the ferroelectric superlattice material comprises a quantum paraelectric insulator material SrTiO3(abbreviated as STO) and a metallic conductive oxide material SrRuO3(abbreviated SRO).
The strontium titanate/ruthenate strontium ferroelectric superlattice thin film material is characterized in that: the ferroelectric superlattice material has a (001) plane orientation in which strontium titanate and strontium ruthenate are both layered and periodically arranged alternately.
The strontium titanate/ruthenate strontium ferroelectric superlattice thin film material is characterized in that: the ferroelectric superlattice material is formed by alternately arranging ultrathin strontium titanate layers and strontium ruthenate layers to form a periodic microstructure which can be expressed as STO-x/SRO-y, wherein: x represents the periodic thickness of STO, 9, 18, 25 unit cells, i.e. STO thickness of 9, 18 or 25 unit cells per period; y represents the periodic thickness of the SRO, 1 and 2 unit cells respectively, i.e. the thickness of the SRO in each period is 1 or 2 unit cells. The repeating cycle is 23-62 times, and the total thickness of the film is 250 nm.
The strontium titanate/ruthenate strontium ferroelectric superlattice film is characterized in that: the ferroelectric superlattice thin film is grown on an oxide single crystal substrate (such as Nb-SrTiO)3、SrTiO3、LaAlO3Etc.), preferably 0.7 wt.% Nb-SrTiO3A single crystal substrate.
The ferroelectric property of the superlattice film material can be regulated and controlled by the periodic thickness of strontium titanate and strontium ruthenate. The thickness of the fixed strontium ruthenate is 1 unit cell, and when the strontium titanate is 9 unit cells, the remanent polarization is 9.0 mu C/cm2(ii) a When the strontium titanate has 18 unit cells, the remanent polarization is 4.7 μ C/cm2(ii) a When the strontium titanate has 25 unit cells, the remanent polarization is 6.3 μ C/cm2. When the thickness of the strontium titanate is 25 unit cells and the strontium ruthenate is 2 unit cells, the remanent polarization can reach 33.0 mu C/cm2。
The invention also provides a preparation method of the strontium titanate/ruthenate strontium ferroelectric superlattice thin film material, which is characterized by comprising the following specific steps of:
(1) respectively placing strontium titanate target materials and strontium ruthenate target materials in a deposition chamber of pulse laser deposition equipment, placing oxide single crystal substrate materials on a sample seat, and preparing the ferroelectric superlattice material by using a pulse laser deposition method, wherein the molar ratio of the strontium titanate target materials is Sr to Ti to O is 1:1:3, and the molar ratio of the strontium ruthenate target materials is Sr to Ru to O is 1:1: 3;
(2) alternately irradiating the strontium titanate target material and the strontium ruthenate target material by using pulse laser under the conditions that the temperature is 650 ℃ and the oxygen pressure is 20Pa, accurately controlling the thicknesses of the strontium titanate target material and the strontium ruthenate target material according to the respective growth rates of a strontium titanate layer and a strontium ruthenate layer, wherein when the deposition time of the strontium ruthenate layer is 1 second and 2 seconds respectively, the thicknesses of the strontium ruthenate layer are 1 unit cell and 2 unit cells respectively; when the deposition time of the strontium titanate is 4, 8 and 11 seconds, the thickness is 9, 18 and 25 unit cells.
(3) And (3) repeating the process of the step (2) to ensure that the total thickness of the prepared superlattice film is about 250nm (the repetition period is 23-62 times).
As a preferred technical scheme:
in the step (1), Nb-SrTiO is used3Using single crystal slices as substrate materials, respectively cleaning the single crystal slices by using acetone and ethanol for 10 minutes, then placing the substrates on a sample seat in a deposition chamber, heating the substrates to 750 ℃ under the oxygen pressure of 20Pa, and preserving the heat for 30 minutes;
in the step (2), the temperature of the substrate is reduced to 650 ℃, the laser frequency of the strontium titanate and the strontium ruthenate target materials is 5Hz under the oxygen pressure of 20Pa, and the energy density is 1.0-1.5J/cm2The distance between the target and the substrate is 4 cm.
In the step (2), when the time for irradiating the strontium titanate and the strontium ruthenate by the pulse laser is 11 seconds and 2 seconds respectively, the STO-25/SRO-2 superlattice material can be obtained, each growth cycle of the superlattice consists of 25 strontium titanate unit cells and 2 strontium ruthenate unit cells, and the repetition frequency in the step (3) is 24 times.
In the step (2), when the time for irradiating the strontium titanate and the strontium ruthenate by the pulse laser is 4 seconds and 1 second respectively, the STO-9/SRO-1 superlattice film material can be obtained, each growth cycle of the superlattice consists of 9 strontium titanate unit cells and 1 strontium ruthenate unit cell, and the repetition frequency in the step (3) is 62 times.
In the step (3), the intermittent time is ensured to be 10 seconds when the strontium titanate and the strontium ruthenate layers are alternately grown.
After the step (3) is finished, the obtained ferroelectric superlattice material is at 5 multiplied by 104And (3) keeping the temperature of the Pa solution at 650 ℃ for 30 minutes under high-purity oxygen, and then cooling the Pa solution to room temperature at the speed of 2-10 ℃/min.
The invention has the advantages that:
1) although neither strontium titanate nor strontium ruthenate is a ferroelectric material, a superlattice thin film material composed of the two materials has ferroelectric polarization performance; 2) because both strontium titanate and strontium ruthenate do not contain lead, the strontium titanate/strontium ruthenate ferroelectric superlattice film is a lead-free ferroelectric material; 3) the remanent polarization of the material is as high as 33.0 mu C/cm2The lead-free ferroelectric film material is 750 percent higher than a typical lead-free ferroelectric material barium titanate film, even can be compared with the PZT lead-based ferroelectric film material commonly used at present, so the strontium titanate/ruthenate strontium ferroelectric superlattice film material is a high-performance lead-free ferroelectric material.
The invention adopts a pulse laser deposition method to prepare strontium titanate and strontium ruthenate ferroelectric superlattice films. In the preparation process, the thicknesses of the strontium titanate layer and the strontium ruthenate layer can be accurately regulated and controlled, so that the ferroelectric, dielectric and other properties of the superlattice film can be effectively regulated and controlled. The thickness of the strontium ruthenate layer is controlled to be 1-2 unit cells, and excellent ferroelectric performance can be obtained at room temperature by regulating the thickness of strontium titanate (9, 18 and 25 unit cells respectively). The strontium titanate/ruthenate strontium ferroelectric superlattice film material can be used as a high-performance lead-free ferroelectric material to replace a PZT lead-based ferroelectric film, and in addition, the strontium titanate/ruthenate strontium ferroelectric superlattice film and the preparation technology thereof can be compatible with a semiconductor micromachining process technology, so that the strontium titanate/ruthenate strontium ferroelectric superlattice film material has wide application prospect in the aspects of integrated ferroelectric devices such as ferroelectric random access memories, sensors, actuators, transistor field effect transistors, surface acoustic wave devices, pyroelectric detectors and the like.
Drawings
FIG. 1 shows the present invention at 0.7 wt.% Nb-SrTiO3Schematic microstructure diagram of STO/SRO superlattice thin film prepared on the substrate;
FIG. 2 shows the present invention at 0.7% Nb-SrTiO3STO-25/SRO-1, STO-25/SRO-2 and STO-25/SRO-3 superlattice films and BaTiO prepared on substrate3And SrTiO3An X-ray diffraction pattern of the film;
FIG. 3 is a graph of the present invention at 0.7 wt.% Nb-SrTiO3A transmission electron microscope photograph of the STO-25/SRO-2 superlattice thin film prepared on the substrate, a) a low magnification photograph, b) a high resolution photograph;
FIG. 4 is a graph of the present invention at 0.7 wt.% Nb-SrTiO3Superlattice thin film prepared on substrate and BaTiO3And SrTiO3Electric hysteresis loop of film (a) STO-25/SRO-1, STO-25/SRO-2, SrTiO3Film, (b) STO-9/SRO-1, STO-18/SRO-1 and SrTiO3A film;
FIG. 5 shows the present invention at 0.7% Nb-SrTiO3STO-25/SRO-3 superlattice thin film (a) and BaTiO prepared on substrate3The hysteresis loop of the film (b).
Detailed Description
The following examples further illustrate the invention but are not intended to limit the invention thereto.
Example 1
STO-25/SRO-1 ferroelectric superlattice material
(1) Adding Nb-SrTiO3(001) Cleaning the substrate with acetone and ethanol for 10 min, placing in a deposition chamber, heating to 750 deg.C in vacuum, and maintaining for 30 min;
(2) bombarding a strontium ruthenate target by using pulse laser under the conditions that the deposition temperature is 650 ℃ and the oxygen pressure is 20Pa, so that the Nb-SrTiO target is formed3(001) A strontium ruthenate layer with a thickness of 1 unit cell is deposited on the substrate. Then converting the target material into strontium titanate, and depositing a strontium titanate layer with the thickness of 25 unit cells on the strontium ruthenate layer;
(3) repeating the process (2) for 25 times to obtain the STO-25/SRO-1 ferroelectric superlattice thin film material.
(4) Before the electric performance test, the surface of the obtained ferroelectric superlattice film is coated with a layer with the area of 0.1963mm by magnetron sputtering2The platinum electrode of (1).
The microstructure of the resulting STO-25/SRO-1 superlattice film is shown in FIG. 1, with strontium ruthenate in the superlattice being 1 unit cell thick and strontium titanate being 25 unit cells thick. The superlattice thin film has a (001) plane crystal orientation (fig. 2). The residual polarization intensity of the superlattice material is about 6.3 mu C/cm2(see FIG. 4(a)), and a lead-free ferroelectric material BaTiO3The film (see FIG. 5(b)) shows a 66% increase in contrast.
Example 2
STO-25/SRO-2 ferroelectric superlattice material
(1) Adding Nb-SrTiO3(001) Cleaning the substrate with acetone and ethanol for 10 min, placing in a deposition chamber, heating to 750 deg.C in vacuum, and maintaining for 30 min;
(2) under the conditions of 650 ℃ of deposition temperature and 20Pa of oxygen pressureThe pulse laser bombards the strontium ruthenate target material to ensure that the target material is Nb-SrTiO3(001) A strontium ruthenate layer with a thickness of 2 unit cells is deposited on the substrate. Then bombarding the strontium titanate target material by using pulse laser, and depositing a strontium titanate layer with the thickness of 25 unit cells on the strontium ruthenate layer;
(3) repeating the process (2) 24 times to obtain the STO-25/SRO-2 ferroelectric superlattice thin film material.
(4) Before the electric performance test, the surface of the obtained ferroelectric superlattice film is coated with a layer with the area of 0.1963mm by magnetron sputtering2The platinum electrode of (1).
The resulting STO-25/SRO-2 superlattice has a crystal orientation of (001) plane (FIG. 2), a thickness of 2 units of strontium ruthenate and a thickness of 25 units of strontium titanate in the superlattice, and a transmission electron micrograph of the microstructure is shown in FIG. 3. The superlattice material has excellent room temperature polarization performance and residual polarization intensity of about 33.0 mu C/cm2(see FIG. 4(a)), and BaTiO3The film contrast increased by nearly 750%.
Example 3
STO-18/SRO-1 ferroelectric superlattice material
(1) Adding Nb-SrTiO3(001) Cleaning the substrate with acetone and ethanol for 10 min, placing in a deposition chamber, heating to 750 deg.C in vacuum, and maintaining for 30 min;
(2) bombarding a strontium ruthenate target by using pulse laser under the conditions that the deposition temperature is 650 ℃ and the oxygen pressure is 20Pa, so that the Nb-SrTiO target is formed3(001) A strontium ruthenate layer with a thickness of 1 unit cell is deposited on the substrate. Then bombarding the strontium titanate target material by using pulse laser, and depositing a strontium titanate layer with the thickness of 18 unit cells on the strontium ruthenate layer;
(3) repeating the process (2) 33 times to obtain the STO-18/SRO-1 ferroelectric superlattice thin film material.
(4) Before the electric performance test, the surface of the obtained ferroelectric superlattice film is coated with a layer with the area of 0.1963mm by magnetron sputtering2The platinum electrode of (1).
The resulting STO-18/SRO-1 superlattice has a (001) plane crystal orientation with 1 unit cell thickness of strontium ruthenate and 18 unit cells thickness of strontium titanate in the superlatticeThe structure is shown in figure 1. The residual polarization strength of the superlattice material at room temperature is about 4.7 mu C/cm2(see FIG. 4(b)), and BaTiO3The remanent polarization of the film was comparable.
Example 4
STO-9/SRO-1 ferroelectric superlattice material
(1) Adding Nb-SrTiO3(001) Cleaning the substrate with acetone and ethanol for 10 min, placing in a deposition chamber, heating to 750 deg.C in vacuum, and maintaining for 30 min;
(2) bombarding a strontium ruthenate target by using pulse laser under the conditions that the deposition temperature is 650 ℃ and the oxygen pressure is 20Pa, so that the Nb-SrTiO target is formed3(001) A strontium ruthenate layer with a thickness of 1 unit cell is deposited on the substrate. Then bombarding the strontium titanate target material by using pulse laser, and depositing a strontium titanate layer with the thickness of 9 unit cells on the strontium ruthenate layer;
(3) repeating the process (2) for 62 times to obtain the STO-9/SRO-1 ferroelectric superlattice thin film material.
(4) Before the electric performance test, the surface of the obtained ferroelectric superlattice film is coated with a layer with the area of 0.1963mm by magnetron sputtering2The platinum electrode of (1).
The resulting STO-9/SRO-1 superlattice has a (001) plane crystal orientation, with 1 unit cell thickness of strontium ruthenate and 9 unit cells thickness of strontium titanate in the superlattice, and its structural schematic is shown in FIG. 1. The residual polarization strength of the superlattice material at room temperature is about 9.0 mu C/cm2(see FIG. 4(b)), less pure BaTiO3The remanent polarization of the film increased by nearly 135%.
Comparative example 1
STO-25/SRO-3 ferroelectric superlattice material
(1) Adding Nb-SrTiO3(001) Cleaning the substrate with acetone and ethanol for 10 min, placing in a deposition chamber, heating to 750 deg.C in vacuum, and maintaining for 30 min;
(2) bombarding a strontium ruthenate target by using pulse laser under the conditions that the deposition temperature is 650 ℃ and the oxygen pressure is 20Pa, so that the Nb-SrTiO target is formed3(001) A strontium ruthenate layer with a thickness of 3 unit cells was deposited on the substrate. Then bombarding the strontium titanate target material by pulse laser and depositing on the strontium ruthenate layerA strontium titanate layer with a thickness of 25 unit cells;
(3) repeating the process (2) for 23 times to obtain the STO-25/SRO-3 ferroelectric superlattice material.
(4) Before the electric performance test, the surface of the obtained ferroelectric superlattice film is coated with a layer with the area of 0.1963mm by magnetron sputtering2The platinum electrode of (1).
The resulting STO-25/SRO-3 superlattice has a crystal orientation of (001) plane (see FIG. 2), a thickness of strontium ruthenate of 3 units and a thickness of strontium titanate of 25 units in the superlattice, and its microstructure is shown in FIG. 1. Since the conductivity of the strontium ruthenate layer increases with its thickness, the leakage current of the superlattice thin film material increases significantly, distorting the shape of the hysteresis loop (see fig. 5 (a)). Therefore, the ferroelectric and dielectric properties of the superlattice thin film were not measured. Therefore, the thickness of the strontium ruthenate as a component material of the ferroelectric superlattice should be controlled below 3 unit cells.
Comparative example 2
SrTiO3Ferroelectric thin film material
(1) Adding Nb-SrTiO3(001) Cleaning the substrate with acetone and ethanol for 10 min, placing in a deposition chamber, heating to 750 deg.C in vacuum, and maintaining for 30 min;
(2) bombarding the strontium titanate target material with pulse laser at the deposition temperature of 650 ℃ and the oxygen pressure of 20Pa in the Nb-SrTiO3(001) Depositing a strontium titanate film with the thickness of 250nm on the substrate;
(3) before the electric performance test, the surface of the obtained ferroelectric superlattice film is coated with a layer with the area of 0.1963mm by magnetron sputtering2The platinum electrode of (1).
The resulting strontium titanate thin film had a crystal orientation of the (001) plane (see fig. 2). The polarization of the film changes linearly with the electric field and is therefore not ferroelectric (see fig. 4(a) and (b)).
Comparative example 3
BaTiO3Ferroelectric thin film material
(1) Adding Nb-SrTiO3(001) The substrate was cleaned with acetone and ethanol for 10 minutes, respectively, and then placed in a deposition chamber,raising the temperature to 750 ℃ in vacuum and preserving the temperature for 30 minutes;
(2) bombarding a barium titanate target material by using pulse laser under the conditions that the deposition temperature is 650 ℃ and the oxygen pressure is 20Pa, and depositing the barium titanate target material on the Nb-SrTiO3(001) Depositing a barium titanate film with the thickness of 250nm on the substrate;
(3) before the electrical property test, a layer with the area of 0.1963mm is plated on the surface of the obtained barium titanate film by magnetron sputtering2The platinum electrode of (1).
The resulting barium titanate thin film had a crystal orientation of the (001) plane (see fig. 2). The remanent polarization of the barium titanate film is about 3.8 mu C/cm2(see FIG. 5 (b)). In contrast, the remanent polarization of the strontium titanate/ruthenium acid strontium ferroelectric superlattice is 4.7-33.0 μ C/cm2The addition is increased by 24 to 750 percent,
the above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (9)
1. A strontium titanate/ruthenate strontium ferroelectric superlattice thin film material is characterized in that: the ferroelectric superlattice thin film material is made of a quantum paraelectric insulator material SrTiO3And a metallic conductive oxide material SrRuO3And (4) forming.
2. The strontium titanate/ruthenate strontium ferroelectric superlattice thin film material according to claim 1, characterized in that: the ferroelectric superlattice thin film material has (001) plane crystal orientation, and the strontium titanate/strontium ruthenate are layered and are periodically and alternately arranged.
3. The strontium titanate/ruthenate strontium ferroelectric superlattice thin film material according to claim 1, characterized in that: the ferroelectric superlattice thin film material is represented as STO-x/SRO-y, wherein: STO stands for SrTiO3And x represents the periodic thickness of STO and is 9 and 18 or 25 unit cells; SRO stands for SrRuO3And y represents the periodic thickness of the SRO, being 1 or 2 unit cells.
4. The strontium titanate/ruthenate strontium ferroelectric superlattice thin film material according to claim 1, characterized in that: the ferroelectric superlattice thin film material grows on Nb-SrTiO3、SrTiO3、LaAlO3On an oxide single crystal substrate.
5. The strontium titanate/ruthenate strontium ferroelectric superlattice thin film material according to any one of claims 1-4, characterized in that: the thickness of the ferroelectric superlattice thin film material is 200-300 nm.
6. A method for preparing the strontium titanate/ruthenate ferroelectric superlattice thin film material according to claim 1, which is characterized by comprising the following steps:
(1) firstly, placing strontium titanate and strontium ruthenate target materials in a deposition chamber of pulsed laser deposition equipment, then placing a substrate material on a sample seat in the deposition chamber, wherein the molar ratio of the strontium titanate target materials is Sr to Ti to O is 1:1:3, and the molar ratio of the strontium ruthenate target materials is Sr to Ru to O is 1:1: 3;
(2) bombarding the strontium ruthenate target material by using pulse laser for 1 or 2 seconds at the temperature of 650 ℃ and the oxygen pressure of 20Pa in the Nb-SrTiO3(001) Depositing a strontium ruthenate layer with the thickness of 1 or 2 unit cells on a substrate;
(3) growing a strontium titanate layer on the substrate obtained in the step (2), and bombarding a strontium titanate target material by using pulse laser for 4, 8 or 11 seconds under the conditions that the deposition temperature is 650 ℃ and the oxygen pressure is 20Pa, so that the thickness of the strontium titanate layer is 9, 18 or 25 unit cells;
(4) and (3) ensuring that the total thickness of the prepared superlattice is 250nm by repeating the processes in the steps (2) and (3).
7. The method for preparing strontium titanate/ruthenate strontium ferroelectric superlattice thin film material according to claim 6, characterized in that: step (2),(3) In (4), the laser energy is 1.0-1.5J/cm2And the distance between the target and the substrate is 4 cm.
8. The method for preparing strontium titanate/ruthenate strontium ferroelectric superlattice thin film material according to claim 6, characterized in that: when the strontium titanate layer and the strontium ruthenate layer are alternately grown, the intermittent time is ensured to be 10 seconds.
9. The method for preparing strontium titanate/ruthenate strontium ferroelectric superlattice thin film material according to claim 6, characterized in that: in the step (4), after the film formation is finished, the prepared superlattice thin film material is processed at 650 ℃ and 5 multiplied by 104Annealing for 30 minutes under high-purity oxygen of Pa, and then cooling to room temperature at the speed of 2-10 ℃/min.
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